1. Field of the Invention
The present invention relates to an inkjet printer, and more particularly, to a thermal inkjet printhead having an improved ejection property and stable structure.
2. Description of the Related Art
In general, inkjet printers are devices that eject ink droplets from an inkjet printhead onto desired positions of a printing medium in order to form an image of certain color. Examples of such inkjet printers include a shuttle type inkjet printer and a line printing type inkjet printer. A shuttle type inkjet printer performs a printing operation by reciprocating an inkjet printhead along a transfer direction perpendicular to the direction of travel of the printing medium. A line printing type inkjet printer on the other hand may achieve higher printing speed by utilizing an array of printheads that spans the width of the printing medium. A line printing type inkjet printer performs a printing operation by moving the printing medium past the stationary printhead array.
Inkjet printheads themselves may be broadly categorized according to their ink ejection mechanism into two types, a thermal type inkjet print head and a piezoelectric type inkjet printhead: A thermal inkjet printhead ejects the ink droplets due to the thermal expansion of ink bubbles while a piezoelectric inkjet printhead ejects ink droplets due to the pressure applied to ink by deformation of a piezoelectric body.
For example, in a thermal inkjet printhead, when a pulse current is supplied to a heater including a heating resistor, the heater generates heat causing the ink near the heater to be instantaneously heated up to approximately 300° C., thereby making the ink boil. The boiling ink evaporates, producing ink bubbles, which continue to expand to exert pressure on the ink filled in an ink chamber. As a result, ink around a nozzle is ejected from the ink chamber in the form of droplets through the nozzle. Such a thermal inkjet printhead generally has a structure that includes a chamber layer and a nozzle layer sequentially stacked on a substrate. An ink feed hole for supplying ink is formed in the substrate, and an ink chamber filled with ink to be ejected is formed in the chamber layer. In addition, a plurality of nozzles through which to eject ink is formed on the nozzle layer.
A trajectory error with respect to an ink droplet can occur, for example, due to a missing nozzle or due to variations in ejection characteristics of the nozzles in the inkjet printhead. A trajectory error can be compensated somewhat in a shuttle type inkjet printer by software-based correction or motion correction of the inkjet printhead since the inkjet printhead of the shuttle type inkjet printer performs a printing operation by moving the printhead. However, the effect of a trajectory error on printing quality may be exacerbated in a line printing type inkjet printer of higher printing speed since in a line printing type inkjet printer the printing operation is performed while moving the printing medium with the array printhead remains stationary. Accordingly, an inkjet printhead having a structure capable of addressing trajectory errors of ink droplets is desirable.